1. Field of the Invention
The present general inventive concept relates to an audio reproducing system, and more particularly, to an active audio matrix decoding method based on positions of speakers and a listener, and an apparatus thereof.
2. Description of the Related Art
Generally, when movies are watched at home, ground wave broadcasting has been the main source of these movies in the past. However, video tapes, video discs, and satellite broadcasting have recently gained popularity and widespread use. Accordingly, original sound of movies can be enjoyed at home. In the video tapes, video discs, and satellite broadcastings which provide the original sound, a multi-channel audio signal is encoded into a 2-channel audio signal through matrix processing. Also, the 2-channel audio signal encoded through the matrix processing can be reproduced as a stereo signal. Furthermore, when a dedicated decoder is used, a 5-channel audio signal, including a front left (L) channel, a center (C) channel, a front right (R) channel, a left surround (Ls) channel, and a right surround (Rs) channel, is restored. In this 5-channel audio signal, the center channel signal plays a role in obtaining a correct localization that is for clearness of sound, and the surround channel signal(s) improve the actual feeling or perception of moving sound, environment sound, and echo sound.
A conventional matrix decoder generates a center channel and a surround channel by using a sum and a difference of two channel signals. An audio matrix in which matrix characteristics are not changed is known as a passive matrix decoder.
In each channel signal separated by the passive matrix decoder, when encoding is performed, other channel audio signals are scaled down and linearly combined together. Accordingly, the separation between the channels is low in the channel signals output through the conventional passive matrix decoder such that sound localization is not performed clearly. An active matrix decoder adaptively changes the matrix characteristics in order to improve separation among 2-channel matrix encoding signals.
U.S. Pat. No. 4,779,260 filed Feb. 6, 1986 entitled a “variable matrix decoder,” and WO 02/19768 A 2 filed Aug. 31, 2000, entitled a “method and apparatus for audio matrix decoding” describe a conventional matrix decoder.
FIG. 1 illustrates the conventional matrix decoder. In the conventional matrix decoder, gain function units 110′ and 116 clip an input signal in order to balance levels of a stereo signal (Rt, Lt). A passive matrix function unit 120′ outputs a passive matrix signal from the stereo signal (R′t, L′t) output from the gain function units 110′ and 116. The passive matrix function unit 120′ also includes scaling function units 122 and 124, and combining function units 126 and 128. A variable gain signal generation unit 130′ generates 6 control signals (gL, gR, gF, gB, gLB, gRB) in response to the passive matrix signal generated in the passive matrix function unit 120′. A matrix coefficient generation unit 132 generates 12 matrix coefficients in response to the 6 control signals generated in the variable gain signal generation unit 130′. An adaptive matrix function unit 114 generates output signals (L, C, R, L, Ls, Rs) in response to the input stereo signal (R′t, L′t) and the matrix coefficients generated in the matrix coefficient generation unit 132. The variable gain signal generation unit 130′ monitors the level of each channel signal, and by calculating an optimum linear coefficient value with respect to the level of the monitored channel signal, reconstructs a multi-channel audio signal. The matrix coefficient generation unit 132 nonlinearly increases the level of a channel having a highest level.
However, the conventional matrix decoder illustrated in FIG. 1 does not consider positions of virtual sound sources generated in a multi-channel environment such that localization of a sound image cannot be performed accurately. Also, since it is difficult to express a positional change of a sound source moving in a virtual space, the capability of dynamically expressing a sound image is insufficient.